I've never even heard of gate 272. Is that meant to be D72?

Even with checked luggage, a non-NA passport, and a visit to secondary the most I've ever known to take getting through YYZ is 90 mins. Normal with non-priority luggage and no extra inspections etc... is about 30-45 mins from wheels down, could be a bit faster on what I assume is a E75/190/CRA. Note these times are based on people who generally walk faster than people walking on travelators so YMMV.

UPX is about 10-15 mins away and reasonably well signposted (compared to say the monorail) from T1 and fairly regular so you should be fine. But as you say, if you are significantly delayed or get grounded for a red alert (my favourite delay at YYZ) you may be spending a night downtown. If there is no way you're going to make the train it might be cheaper to check-out one of the two airport hotels accessible via the monorail.