I am an F-1 student in the US and I traveled to Canada on a single entry visit visa in August. I came back to the US after that trip, and I am planning on making another visit to Canada this December.
I read on the Canadian visa website FAQ that holders of single entry visas can re-enter Canada if they visit the US during that time period:
A single-entry visa allows you to enter Canada once.
When you arrive at the point of entry in Canada, an officer of the Canada Border Services Agency will make sure you meet the requirements to enter Canada.
The officer will authorize your stay by placing a stamp in your passport and/or issuing an additional document.
If there is no stamp, a handwritten date or document in your passport, your temporary resident status will expiresix months from the day you arrived in Canada.
If you were given a visitor record, student or work permit, the expiry date is marked on the document.
If you leave Canada during your authorized stay, you must get a new visitor visa to re-enter Canada.
There are two exceptions: you can visit the United States or Saint-Pierre et Miquelon and return to Canada without getting a new visa, as long as you:
return within the initial period authorized by the immigration officer or
have a valid visitor record, work permit, study permit, or a temporary resident permit (authorizing re-entry) and return within the initial period authorized by the officer.
I'm unsure of the intent of this rule, because I came "home" to the US and I'm planning another trip to Canada within the validity period of my existing visit visa. I also don't have my passport in hand to see if the immigration officer wrote an earlier expiration date on my visa as I left Canada (I can't think of a reason why this would be done, but I can't be 100% sure).
Does anyone know for sure whether or not I will be able to re-enter Canada on my existing single entry visa?
You have to look at the Canadian stamp on the passport. If there is no date entered, then you can re-admitted on the single entry TRV up unto 6 months of the original entry. If there is a date as to when you must leave Canada, then you would have to return before that date.