US citizen resident in Canada wants TFSAs -- US tax exempts?

[kal2]

I am told by my bank that I can set up a self-directed TFSA that will let me use US$ located in a Canadian bank to buy US tax exempt bonds through a Canadian broker to hold in a Canadian TFSA. If I avoid the private activity types of bonds, would these TFSAs be tax exempt in the US because of the nature of the assets in them? Or is there something about not holding tax exempt bonds directly, outside a registered account, that would trigger US income tax liability anyway? I can't find anything that speaks directly to this approach, but it seems a bit too obvious to work. Views on the impact of doing this would be appreciated. (I am aware of continuing discussion of forcing some tax liability in the US on tax exempt bonds, but it does not seem to be anything that is currently pending or agreed upon.)