I use a USA TA have for many years
Many line now they will accept CAD or USD fro US agents it was not always the case
We get PPG & small OBC but if things go wrong she goes to bat for us
over the years we have gotten free upgrades, price drops she deals with before I even know about it
Look for agencies that belong to a Consortium they get deals from the cruise lines they can pass on to their clients
Ask fellow cruisers onboard if they are happy with their agent & perks