So you have two different factors at play, and I'll answer both of them
You're Canadian, traveling on a Canadian passport (visa requirement)
You don't need a visa or ESTA to travel to the US
You are married to a US citizen and both of you are travelling from the UK (COVID-related ban)
Travelers from the UK were banned from entry under PP 10143 even those who ...
What's my chance of being admitted to USA if I don't have an exit train booked?
You're unlikely to be allowed on the plane in the first place, as Timatic states that a return ticket is mandatory for ESTA passengers:
A return/onward ticket (or electronic ticket record) must be to a final destination country other than Canada, Mexico or contiguous (adjacent) ...