
Canadian whisky is a typically light-bodied blended whisky — a near-neutral, mostly-corn base whisky blended with smaller amounts of more flavorful "flavoring" whiskies, often rye. It’s built for easy mixing rather than bold flavor.
Light and smooth is the whole brief, so almost any gentle whisky does the job. Going heavier is the risk: a spicier or oakier bottle takes over a long drink built to stay quiet.
US rye is at least 51% rye in new charred oak: drier, more peppery and distinctly fuller. A cocktail built for light Canadian sharpens up with it and wants about a quarter less.
Bourbon is sweeter and fuller, Canadian lighter and smoother. In a highball you barely hear it; in a stirred drink bourbon steps forward, and where there is vermouth it wants about a barspoon less.
"Canadian whisky = rye whiskey"
In Canada "rye" is a historical name for the local whisky, not a mash bill: there may be almost no rye in the bottle. A recipe written for US rye comes out softer and sweeter on it.