My personal choice would probably be 30-06 .The flat shooting cartidge is useful and has plenty of knockdown power. caribou are generally weak animals but they typically live in wide open country and can travel very far with a poorly placed shot. I would recommend shooting sticks or a bipod as sometimes hunting caribou you can’t get within 250 yards due to terrain.
30-06 would be my selection of the 2. Better glass and a tad more energy. Not saying the 7mm-08 wouldn't do the trick, I'd just take the best glass with the most energy I could get on such an important hunt.
I have hunted Caribou 2 times in Quebec, Delay River 1 trip. Hunting migration trails mostly. Hide behind a rock or spruce tree and shot them at 20 yds. with a bow. 7 of 11 Caribou killed in camp were Bow Kills.
I have hunted Newfoundland 2 times. Hunted Moose. But seen a lot of Caribou, They seem to stay on high ridges. Seen a lot near Buchans on a hunt there. Caribou season was next week. Seen caribou from 50 yards to 1000 yds. All moose we seen was long range, 800 yds. and beyond. The weather was warm Bulls would not answer calls. South of Red Indian Lake seen moose no bulls, Brother and I had Bull/ Calf tags. All areas we hunted in Newfoundland had many places my 550 yard range finder was useless.
Take the 30-06 and may wish you had more rifle when it comes shooting time.
If you are driving, Be sure to get Ferry Reservations in advance, And plan time in your drive to arrive early. I suggest book a 11:00 pm ferry crossing. Get a room sleep on the ferry, Be ready to drive in the morning. Going and on return trip too. Be sure to set up a GPS and put the coordinates of the gate at the Sidney terminal in. My GPS took us right to the gate. Bon Voyage