I’m confused by your post because you’re throwing a bunch of random facts in here about the U.S. and it’s not clear exactly what advice you’re looking for. Are you interested only in Germany, or in the U.S., or “another country”? You mentioned all three.

Assuming you’re only interested in Germany, you need to check with a German accountant. Canada retains the right to tax the RRSP and the treaty says that Germany shall grant a foreign tax credit for any tax paid to Canada on “pensions”. However, this depends on Germany’s interpretation under its local laws and whether it would view the RRSP as a pension at the time or after death. It also may be the case that Germany does not grant a credit against inheritance taxes. Check with a German accountant.