Starbucks, McDonald's, and many of the big box stores like Walmart, Lowes, Home Depot, Staples (may) offer free wifi in Canada. Welcome centers and other "touristy" places may also offer it. No guarantees.
If you're driving via Hwy 97 (AlCan/Alaska Highway) there aren't many cell towers out there once you get past Dawson Creek, except in the towns and cities. The main cell tower coverage up there is by Bell Mobility, so if you have a US service provider that has a reciprocal agreement with Bell Mobility Canada, your phone may work in a "roaming" sense, but as there aren't many towers, cell service may be spotty/unreliable. Alternately, you could purchase a cheap prepaid Bell-based SIM card, add some funds, and get coverage that way.
3 years ago we found out the hard way that Rogers based cell service is pretty much shut out along Hwy 97.
When you hit the Alaska border, then your own cell tower infrastructure will take over, and you'll probably have better coverage.
