Fongo will probably be your potentially cheapest bet as you can do calling and SMS, but their outbound rates are a little steep for their non-free termination from a VoIP pricing standpoint. However, they do offer E911, so you can at least still make emergency calls if needed. You should be able to port your number.
VOIP.ms would be another good option for PAYGO as they also support SMS with certain phone numbers and offer E911, but
you'll need a dedicated app for texting separate from the
softphone app you'll need as well. Their rates are quite a bit lower per minute than Fongo, and the SMS is free for the time. You can port your number, but I can't promise you'll be able to text with it. I'm about 80% certain that you have to purchase a DID that supports texting from them for SMS support, but you can check with customer support there and ask.
There's also
Line2, but you lose E911 support and it's a flat $10/month for "unlimited" use and you can port your number. You get SMS support, too.
Those are your three best bets for Canadian VoIP service with decent rates and SMS support. Now that I have that out of the way, it's worth pointing out that VoIP doesn't always work the best over WiFi, especially public WiFi which can be overloaded or throttled or have interference or or or.... It is a technology that works best on wired networks. I know that everyone and their dog has a wireless VoIP app/service from Apple's Facetime to Zoiper and everything inbetween... but it's not always going to be reliable. Understand this. Expect this. Tolerate this if you're going to go this route. From a network security standpoint, it's usually not wise to randomly connect promiscuously to every open WiFi hotspot, either. You don't know who or what is there listening, and it's not hard to MITM these sorts of things.
Can it be done? Yeah, kinda. There's services and apps for it. If you need to communicate in a timely fashion? It's not going to be ideal. If you barely use your phone as it is, perhaps you'd be better served switching your carrier to
7-11 SpeakOut Wireless or
PetroCanada Mobility if you're on some expensive monthly service plan.
If you want a guide on how to better leverage this technology to save money, give
the guide (
unabridged) a read.