Peter,
I had to deal with this situation when we were fulltiming and you are quite right, as Canadians we need to show a Canadian physicial address for the very important reasons you meantioned earlier.
In Canada, because Medicare is a Provincial jurisdiction, you need to show a physical address in the Province you choose to be your home base, unlike our American colleagues who don't require a physical address because medical insurance is handled differently.
In Canada you need to demonstrate that you have a Province of domicile, which means not only a physical address, but a local bank account and sometimes other forms of ties to a community.
For a time I used the physical address of a trusted relative, which could have been an actual emergency home if required, because they had a spare bedroom.
Something to consider, is if you are fulltiming, and become ill while in the U.S. and need to be repatriated for intensive medical care, you may want to have a contingency plan for emergency housing. In an emergency situation, in the middle of winter when one spouse is being transported to a hospital, the oether spouse doesn't want to be searching for a motel or other place to live temprarily.
That being said, the UPS Store (formerly MailBoxes Etc) is your best bet. They provide you with an actual physical address, and your milbox number is shown as a suite or appt number, thereby most likely satisfying bureaucratic requirements for your drivers license, passport and bank ID.
They will forward your mail to any location using UPS or other courrier service, and you pay the forwarding costs.
The Province you choose as your base will determine the number of days you can be out of the Province and continue to maintain Medicare benefits. It varies from Province to Province and if you are not familiar with those rules, let me know and I'll elaborate.
The other side of the coin is the number of days you spend in the U.S. without being required to submit an IRS tax return. Are you familiar with the IRS rule concerning
Closer Connectionto Another Country? and it's
accompanying form?