applying visitor visa at port of entry?

[Yi]

I recently read the instruction for applying TRV out side of Canada. In "where do I apply" section, it mentions "If you are from the US, Greenland or St. Pierre and Miquelon, you can apply at a Canadian port of entry". Does this mean I can apply my travel visitor visa at port of entry if I am driving pass US/CA border?

[Suin]

if you are a citizen of the US you don't need visa to cross the border to Canada

[accreddy]

You need to apply for TRV atleast 1 month prior to your intended departure if you are not from a visa-exempt country. You can do that at a Canadian Consulate office.

The immigration officer (IO) at port-of-entry decides whether to let you in or not (even with a valid TRV).