Traveling from US to Canada with COVID medical exemption?

Hi all! I was asked to travel to my company’s HQ office in Canada for work sometime in July yesterday, and while it’s not 100% required, it would be very helpful for me to go, and I would really like to. Unfortunately due to family medical history of recurring adverse reactions to 💉, I will be traveling with a medical excuse letter rather than the vaccine passport. Although the Canadian gov website says that some med exemptions are accepted, it is up to the border patrol agent you end up with to determine whether your letter is sufficient, and I am worried as to whether I will be able to get into Canada with this as they seem to be very strict.

Does anyone have experience traveling to Canada from the US with a med exemption/med excuse letter? Also, do they check these letters in the US before boarding the plane, or once you land in Canada?

I’m so scared of getting stuck in Canada/forced to 2 week quarantine or getting on the plane only for them to turn me down when I arrive and send me right back, but unfortunately the vaccine is not an option for me. There is essentially no information detailing others experiences on the internet so hoping i can find some information here. Thanks in advance for any feedback you have!

Edit to add: I am a US citizen, adding as I realize this can impact the requirements