Hi
I think that I rather go with what CIC says, rather than the information that you are giving about returning from Mexico without a valid TRV. http://www.cic.gc.ca/english/helpcentre/answer.asp?q=417&t=16
What kind of visa should I get?
If you are a citizen of a visa required country you should apply for a temporary resident visa (commonly known as a visitor visa). There are two types: a single-entry visa and a multiple-entry visa. Both are valid for a fixed period and cannot be used after they expire.
A multiple-entry visa lets you enter and leave Canada repeatedly while it is valid. It can be valid for up to 10 years, or one month before your passport expires, whichever is earlier. You must arrive in Canada on or before the expiry date on your visa.
A single-entry visa allows you to enter Canada only one time. Once you have left Canada, excluding travel to the United States and St. Pierre and Miquelon, you will need a new visa to travel back to and enter Canada.
If your visa is still valid and you are travelling only and directly to the United States (including its Territories and Possessions) or St. Pierre and Miquelon, you do not need a new temporary resident visa to return to Canada. If your visa expires prior to returning to Canada from this area, and you are not in possession of a valid visitor record, work permit, study permit, or temporary resident permit (authorising re-entry), you will need to obtain a new temporary resident visa.
