I have some VTI in my USD RRSP. I haven't been contributing lately because of the exchange rate, but whenever my USD dividends add up to $1000 cash in the account, I buy a few more.
I also own about the same amount of VUN in my CAD RRSP. I'll probably keep adding to that with new contributions, until the dollar rebounds (though that could take a while!)
From what I've read on CCP, unless your contributions are significant (5 figures) and you can do Norbert's gambit, which I don't think my bank (TD) allows, then VUN isn't costing much more than VTI, and it's more convenient. So I'm sticking with the simplicity of VUN for now.