Depends on how frequently you travel to the US. If you are vaccinated with one of the approved vaccinations in Canada and it's been over 2 weeks since your last dose it shouldn't be an issue.
Yes weekly once itself is enough. Many even travel once in 2 weeks or once in a month too and they dont get asked for quarantine/test.
You should be good to go. No issues for sure. Yes you are exempt as long as you travel for work purpose.