Given a travel related situation, and given a specific question about the situation, summarize the question into a title

Background:

I was originally booked on WestJet from Boston to Glasgow through Halifax. This week, they informed me the BOS -> YHZ flight is canceled, and are wanting to route me BOS -> YYZ -> YHZ -> GLA, doubling the length of the itinerary.

I've called WestJet and they say they can't come up with anything better, so I'm looking for other alternatives.

One possibility is to book a flight on a separate airline from BOS -> YHZ, then take the original YHZ -> GLA flight (after telling WestJet that's what I'm doing, to avoid being seen as a no-show when I don't get on the plane in BOS; the agent I talked to said this would be possible).

The concern is that I will be traveling with checked bags, and these would be two separate tickets, so I'm assuming I will need to clear customs in YHZ, collect my bags, and then re-check them and go through security again, and I don't know how long that will take. Assuming nothing changes (and my faith in that is...tentative, at best), I will have 1 hour 50 minutes between the flights.

Questions:

Are my assumptions correct? I will need to collect bags, clear customs, re-check the bags, clear security?
How long does that process normally take? The flight from Boston is a small plane, arriving at 9 PM on a Sunday.
How long might that process take in the worst case scenario? (I mean, I suppose the worst case is it takes days because something goes horribly wrong, so I guess I'm really looking for an idea of what's a reasonable upper limit...)
It might be possible to get NEXUS before the trip. How much will that affect things?
Customs for connections through Halifax with checked bags and separate tickets