They probably don't want people to or know about swapping out the SIM from the TCU. And, I'm guessing they don't want to be in the business of coming up w/support documentation about which carrier, which plan, frequencies, setup, etc. besides any carrier specific wonkiness there might be.
https://web.archive.org/web/20161231011 ... p?p=148255 shows what the old 2G TCU looked like inside.
Anyway, if I were in Canada and wanted it to work so badly, if nobody has reported yet on whether it works or not, access the TCU, determine what size SIM you need and try putting in one of the right size. It looks like there's some carrier selection screen on the nav system. I sure hope the TCU isn't carrier locked (e.g. to AT&T). That would be so stupid as it'd only make sense for phones coming from carriers, esp. subsidized ones.