Customs for connections through Halifax with checked bags and separate tickets

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?

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Do you go through customs twice on connecting flights?

You only go through once. If you connect through another country, you will just have to go through security and not customs. Incorrect, it all depends on the country and the airlines you're traveling with. Remember customs and immigration are different things and in some cases you'll clear then in different airports.

Do you have to recheck baggage on connecting flights in Canada?

Same terminal connections No terminal changes, and no bags to recheck as they'll automatically be sent to your next Air Canada flight.

Do I have to go through customs for a connecting flight in Canada?

If your airline offers the option of automatically transferring your luggage and you have a boarding pass for your connecting flight, you will be asked to proceed via a connecting flights corridor, avoiding Canadian customs. You will, however, have to go through U.S. customs.

Do you take your checked bag through customs?

Checking my baggage through to my final destination. When entering the United States from overseas, you must obtain your luggage and bring them through Customs and Border Protection (CBP). You will need to check them back into the airlines to make your next flight.

Flying Alone for the First Time | Connecting Flight Procedure | How to Catch a Connecting Flight

Sources: Stack Exchange - This article follows the attribution requirements of Stack Exchange and is licensed under CC BY-SA 3.0.

Images: ROMAN ODINTSOV, Andrea Piacquadio, Andrea Piacquadio, Enrique Hoyos