At the time of writing, the Canadian dollar is worth roughly $0.75 U.S.
Now, it's not possible for you to accurately predict what it'll be worth in, say, ten years. Maybe it'll be worth $0.50 U.S. Maybe $0.67. Maybe $1.00.
Additionally, you can't know in advance if the Canadian economy will grow faster than the U.S., or slower, or by how much.
Let's say you don't want to make a prediction. You just want to invest 50% of your money in Canadian stocks, 50% in U.S. Great. Do that, and don't worry about the current interest rates.
Let's say that you do want to make a prediction. You are firmly of the belief that the Canadian dollar will be worth $1.00 U.S. dollar in approximately ten years. And furthermore, the Canadian economy and the U.S. economy will grow at roughly equal rates, in their local currencies. Great. You should put more of your money in Canadian stocks.
Let's say that you want to make a prediction. The Canadian economy is tanking. It's going to be worth $0.67 or less in ten years. And on top of that, the U.S. economy is primed for growth. It's going to grow far faster than the Canadian economy. In that case, you want to invest mostly in U.S. stocks.
Let's get more complicated. You think the Canadian dollar is going to recover, but boy, maple syrup futures are in trouble. The next decade is all about Micky Mouse. Now what should you do? Well, it depends on how fast the U.S. economy expands, compared to the currency difference.
What should you do? I can't tell you that because I can't predict the future. What did I do? I bought 25% Canadian stocks, 25% U.S. stocks, 25% world stocks, and 25% Canadian bonds (roughly), back when the Canadian dollar was stronger. What am I doing now? Same thing. I don't know enough about the respective economies to judge. If I had a firm opinion, though, I'd certainly be happy to change my percentages a little. Not a lot, but a little.