Canada is enormous, and what you see depends on the month. The lakes of the Rockies thaw to that milky turquoise in summer, larches turn gold for a few weeks in September, and polar bears gather at Churchill only in October and November.
For a first trip we pair the Rockies with the Pacific coast: Banff, Lake Louise and Jasper, then Vancouver and the wild west coast of Vancouver Island around Tofino. It works from June to early October and suits families as well as couples.
The caveat is popularity. Lake Louise and Moraine Lake are busy in July and August, and Moraine Lake Road is closed to private cars, so the shuttles need booking. Stay at the lakes themselves and you see them before and after the crowds.