Cell service in general and Canadians in particular

Being from Canada, I turn off my phone when I cross the border in a southerly direction, to avoid roaming fees (though they're not as onerous as they were). Now that we're venturing into the high peaks, and winter is coming, I'm wondering whether I ought to have some emergency comms device.

• In general, is there a cell provider that gives better service? AFAIK AT&T and T-Mobile use GSM (the kind of phone Canadians have), while Sprint, Verizon and US Cellular use CDMA (needs different phone hardware).
• Canadians, do you carry your phone and switch to roaming on the fly if necessary? If so is the GSM voice service acceptable? I have a Virgin SIM and Mrs. Spork has Koodoo, I wonder if they use the same physical network in the ADKs?
• If it's strictly for emergencies only, perhaps better to carry a VHF radio? I'm planning some small craft activity in the Atlantic next summer, so I need one anyway.

Touch wood, we don't actually need any of this stuff :)