Don't let the tax tail wag the dog.
VUN in your TFSA is the same as VUN in your RSP - you pay the US dividend tax regardless. Capital gains, however, are tax free in your TFSA, but are taxable at your income tax rate when you take income from your RSP.
VUN in a taxable account also has capital gains taxes applicable, even if you claim the dividend credit, don't forget that too.
We are debating this now for my low income partner - does it make sense for them to start a taxable account (and hold VCN), or start filling their RSP?...