I have a valid Study Permit and a student visa (S-1 TRV) for Canada, but I no longer attend the university in Canada and have transferred to a college in America. Can I use my student visa to enter Canada as a tourist or do I need to separately apply for a tourist visa?
Canada does not have a separate Student Visa. When you apply to study in Canada you are issued a Temporary Residence Visa (a normal visitor visa) and a letter. The letter is exchanged at the border for a Study Permit, which, together with the Temporary Residence Visa allows you to study in Canada.
If you decline to study, or finish your course, you can still use the visitor visa for tourism purposes while it is valid.
To answer my own question after entering Canada a couple of times on the student visa as a visitor: yes. One border officer said that as long as the Student Visa is valid it can be used a Tourist Visa since they're both a TRV. I did end up getting a tourist visa eventually since I wanted a longer validity period.
As you are no longer enrolled, your student visa is invalid and cannot be used for travel to Canada; as it only allows travel for the purposes of studies.
If otherwise ineligible, you will have to apply for a normal visit/tourist visa to Canada.
Remember, a visa is not a right to enter the country. It is a permit to request entry based on the premises under which the visa (permission) is granted.