I understand that others with Nexus have been able to connect to CBSA after crossing north of Boundary Passage.
John here is the (official) link to
How to Use NEXUS to Enter Canada. Scroll way down to
Marine: Contact the Telephone Reporting Centre.
I do not have NEXUS as the closest interview site for me is at the Vancouver airport which is a full day car ride, ferry ride and bus ride for me.
Also after talking to several skippers that have used NEXUS, it may actually take longer to clear customs.
As stated in the link, the operator (skipper) must call the centre between 30 minutes and 4 hours before arriving in Canada. In the call, the operator must provide the name and location of the landing site of arrival and
the estimated time of arrival. The vessel must then physically proceed to that landing site and be there at
the estimated arrival time. The link goes on to say: If a border officer is not waiting at the landing site to meet the boat at
the estimated time of arrival, you may continue to your final destination.
So the morale of the story is: you still have to physically go to the landing site and if you are early you would have to wait before you can carry on with your trip. The advantage is there are far more NEXUS landing sites than without. However in IMHO those sites are not convenient locations at least not on the West Coast.