applying for canadian TRV at port of entry?

[confused]

I reside in the US as a temporary worker and have an official visit to canada for a couple of days. I have a pending I-485 adjustment of status as well.

I read a single line in the canadian temporary resident visa guide that one can apply for this visa at a canadian port of entry if they are from the U.S. Is this true for non-US citizens and non-residents?

thanks in advance for any help.
best