You already know this but T3 does not have a sterile transfer from US arrivals to international departures. As you already noted (unlike with AC) you must be admitted into Canada. There is a Sheraton hotel at T3 as well as other close hotels but until July 5 you are supposed to quarantine at a hotel for 3 days for up to $2,000. My guess is if you demonstrate that you will quarantine if staying overnight then you should be ok or if you have an onward connecting boarding pass. Again unlike with AC I don’t believe your luggage automatically transfers at T3. Until July 6 I would avoid transiting in Canada.