Curiousnomad, let me see if I can help you out here. The first thing that jumps out at me is data usage for your line and your buddy's, and the mention that you both extensively use it for navigation. Now, I understand the need for and desire to not cut back on mobile data usage given your situation, but I'm going to throw something out there that's worth investigating anyway.
Live downloaded GPS maps waste a huge amount of data. Your buddy's data usage attests to that, as does your Canadian usage. Given how expensive data can be, it's best to save that data for instances where you actually
need it. Enter Sygic's offline GPS maps. In your case (and possibly your buddy's as well) specifically,
Sygic Fleet Truck Navigation. It's $139 for the North America maps, but there's free updates and given how much you're getting eaten alive in data usage it might pay for itself rather quickly. If your friend does a lot of driving and navigation but doesn't need the truck path restriction, there's
Sygic's standard offline GPS Navigation available for significantly cheaper. As for reading, text is text and text doesn't take up much room or data. If you use a browser like
Dolphin that can disable downloading images while browsing or use an app like
Pocket while on the US side of the border to download what you're wanting to read in advance, that would help put a major dent in your Canadian data usage, or even just data usage in general. If you're mobile, and you're only interested in the text, there's no sense in you paying the bandwidth costs to download the fat, worthless but pretty graphic assets for all these various website templates.
As for the service itself, I am assuming everything is being billed through Verizon. You also didn't specify the type of smartphones you have. I'm honestly and genuinely hoping you're using Android devices and not Apple (especially in the case of the Sygic fleet maps).
A few suggestions and thoughts, however. Ditch the data service on the tablet and do WiFi only on it. If you're on an Android smartphone, it's going to be trivial to do tethering and get a WiFi hotspot going on it,
especially since you're on Verizon. Data is data, after all, and you're already paying for 6GB worth of it plus $25 for every 100MB bucket of Canadian data, and I doubt your tablet (and laptop potentially if you have one) is ever more than a few feet apart from your smartphone. Just kick the WiFi hotspot on with your smartphone while you're in the US when you want data access from the tablet (mostly to save battery life versus running it all the time). That should make at least a $35 dent in the bill, which is a move in the right direction with minimal inconvenience.
You didn't mention if your friend is US only, or wanders up North as well. Now if he's US only, depending on his phone (this would be more problematic with an LTE handset as Verizon LTE devices aren't permitted to activate on Verizon MVNOs and flashing to make them work makes them unreliable), and his need for LTE data and speeds (which would likely be greatly reduced using an offline navigation app like Sygic), there might be the option of moving him off to
Page Plus' Talk & Text 1200 Plan, which might save you an extra $10 a month over a second line on the Verizon account... but that's assuming a lot of potential things that would go in favor of this sort of transition, like the reduced data usage from offline map usage. Page Plus or any other MVNO is clearly
not an option for you, and the extra $10 a month for the hassles this path might open up just might not be worth it for you. Truthfully, you probably need to stick with Verizon.
As for the Canadian data end, it might be worth looking into a cheap Android device and
Virgin Mobile Canada Prepaid. The
coverage map looks favorable to your needs, and
comparable to Rogers for your area if not better for Sask. They have a
500MB for $20CAD prepaid data bucket, and also permit data tethering. It looks like their cheapest prepaid Android handset that can do WiFi tethering is the
Alcatel Idol Mini at $99CAD, but you might be able to pick up something used for cheaper with a little pre-planning and effort. After all, they're a GSM provider and theoretically any carrier unlocked GSM handset with WiFi should work. If they will let you pair their data bucket add-ons with their pay by the minute calling, that should keep you around $25CAD a month for all your Canadian data usage with taxes. Otherwise if you have to use a monthly plan, even with their $10 package with the $20 data, that still keeps you around $35 a month, which is considerably cheaper than $100 a month through Verizon for the same amount of data (or less, technically). Then you just turn off data roaming on your Verizon smartphone, and tether it to the Virgin Mobile phone via WiFi for your data on
it as well as on your tablet or any other devices. That should restrict your Verizon bill to around the $164+tax mark if my math is accurate.
tl;dr: Use offline navigation maps from Sygic. Use WiFi tethering. Use a cheap Android smartphone with Virgin Mobile Canada prepaid for your Canadian data use. Investment cost will be around $250-350ish to enable the savings (so long as you're both already on an Android device and not Apple). That should potentially cut you down to around $200/month or less with an ROI of 3-4 months. I don't think you can do much better in your situation short of shaving data usage down further, but you never know how much data you may actually use outside of navigation until after you gut it from your bill. Who knows, you might be able to get by with 4GB from Verizon between the two of you instead of 6GB. You might only need 100MB a month while in Canada. Don't know until you try.
I don't say this often and I certainly don't like doing so, but this one took a fair bit of effort and research.
Keep my website in mind if you feel inclined to thank me.
https://www.globalgig.com
Nice try, but they don't do Canada and the prices are still steeper than any local mobile data carrier.