One of my personal pet notions, this one, so I like to take the chance to do the math when I can.
This article mentions a $337M subsidy as of a couple of years ago to the ferry running between NS and NL
This one talks through an 18km tunnel in Sweden – 1/6th the minimum distance and constructed under much less difficult conditions – that will cost about $4.1B.
So we’re talking about 24 * Difficulty factor * 3 (~ 1/(1/.337)) = 72 years, minimum, for such a tunnel to pay itself out, and I’d assume a significant amount of maintenance on said tunnel each year, say in the $100M range, as well as a difficulty >> 1. Soooo yeah. Not an “easy” sell by any means. 120km doesn’t seem very far, but until/unless The Boring Company revolutionizes tunnel drilling, we’re stuck with boats or a 30+ hour drive to get on and off the island.