I strongly suspect it's serious fantasy-land stuff. The existing Alaska railroad network is essentially a Seward-Anchorage-Fairbanks line. (We won't count the narrow gauge from Whitehorse.) Anchorage has the only sizable population along that line--300K people live there. So to connect to the Canadian railroad system you'd build about 1,000 miles of track. There are apparently some resource extraction reasons to build such a link but my impression is that it's mostly Alaskan politicians who are interested.