General comments:
Since you live in New Jersey, if you choose to go with an ACA plan you'll need to look at the New Jersey ACA marketplace, which is at
https://www.nj.gov/getcoverednj. The site mentioned by Loren Ver above is the federal site, which New Jersey doesn't use. I don't live in New Jersey, so I'm not familiar with the site, but usually you're able to look at plans, doctors, costs, copays, etc. on the site before signing up for a plan.
The maximum premium subsidy would be at 138% of FPL, which the NJ site above says is $3,048 per month for a family of four. Anything under 150% of FPL will get you maximum CSRs if you sign up for a Silver level plan.
The broker you refer to could be either a private market health insurance broker, or they could be an ACA navigator. In either case, if you like them and think they're doing a good job for you, they can be pretty effective. If you're a cynical control freak like me, then DIY can be a slower, less optimal way to go. :)
You can buy separate ACA policies for each person in your household if you want, and each plan can be a different metal level, or even a different health plan or different insurer if you want. It does make the application process, billing, and tax process more complex because you have to apply four different times, pay four different bills, and receive four different tax forms. But yeah, you can do that if you want - I've done it before when my family was spread out in different zip codes. But in general I wouldn't do it if we were all living in the same house - I'd just pick the plan that worked best for all of us in aggregate because I'd prefer the simplicity of one application, one bill, and one tax form.
Short term plans are usually not bought on the ACA exchange, are cheaper, are not as full-featured as ACA plans, and you don't get any federal tax benefits if you buy one. You can also just sign up for your ACA plan for as long as you'll be here, then cancel it when you get coverage in Canada.
As an aside, reading between the lines here, but you're not eligible to sign up for ACA in February unless you had a qualifying event (leaving your job and moving both qualify; there are more).