My understanding is that as long as it's a Canadian company, whether it's inter-listed in the US or not doesn't matter. Buy the Canadian dollar shares from the Canadian exchange and you're fine. I am thinking of the Canadian banks as an example. They are all Canadian businesses inter-listed on multiple exchanges, but there are no additional tax issues created because of it for Canadian investors.

For TFSA's, I believe the only problems are for dual-citizens of Canada and the US. The IRS doesn't view them as tax-sheltered accounts, regardless of what is held in them in terms of investments.