When a US Amateur operates in Canada, IT and Canadian regs permit some lattitude on their identification. I have read that some will prefix a "VE3" plus their own home callsign (Ontario, meaning I am in Ontario right now, but my real callsign is the following US one) on their callsign, some will simply indicate that that they are mobile in some way, and some may continue to use their regular callsign without indicating that they are mobile? What is actually most commonly done, and what expectations (if any) does the amateur radio community usually expect from mobile operators operating mobile in a friendly foreign nation, particularly Americans operating in Canada?
According to ARRL:
Identification for US amateurs is the US call separated by a stroke and the appropriate Canadian prefix identifier (e.g. N1KB/VE3)
In every case I can think of, one is required to identify the location from which they are transmitting, if it is not in their call sign, or at least a different country. And usually they want more than just the country, they also want to know the location of the country (VE3 in this case). So any amateur should be following this practice, period.
The study course I've been following for the Basic exam says to say (in voice modes) "N1KB mobile VE3". It suggests that for shorter distance communications, you can skip the phoentics and just say vee ee, for the prefix, but should probably use phonetics for other other elements.