Boris Johnson sparked controversy when he announced a feasibility studt would be carried out into a link across the Irish Sea, possibly from Portpatrick to Larne.
But Mr Jack told MSPs on Holyrood's Culture committee that he would instead prefer a link going underwater.
"It's not a bridge that I'm keen on - it's a tunnel," he told MSPs.
"It's not different from the tunnels connecting the Faroes, it's no different from the tunnels underneath the fjords and it removes the problem of Beauford's Dyke and the Word War 11 munitions - 1 million tonnes allegedly were dumped in there.
"It also deals with the problem of weather. It could easily be 100 days a year due to weather of wind that that bridge wouldn't operate.
"The bridge for me is a euphemism for a link which is atunnel - just to be clear about that."
He added that it would be a "less expensive" option to tunnel under the sea given the geography of the area.
He added that there would have to be an upgrade of the A75 and A77 roads to accommodate extra trafiic n the area.
"I see a huge advantage in a tunnel for that, I see a huge advantage in a tunnel for South-west Scotland's economy."
He added: "You will be able to get from carlisle to Belfast or Glasgow to belfast considerably quicker than you can now."