If one spouse is American and the other Canadian, what are the gifting rules for this couple? Is the couple still limited to 26,000 or can they specify that the American is gifting 13,000 and the Canadian gifting 100,000. That is in regard to a property they are selling to their adult child.
The important question isn't nationality as much as it is residency and/or citizenship status. If the Canadian spouse is not a resident of the US or a US Citizen (for instance, pre-immigration) then you are not considered to be a married couple (from a tax perspective, in the US.).
Under that scenario you are taxed on any gift passed between either one of you.
You are given the option of electing to treat the non-resident spouse as a US Resident in some areas of the tax code, see this IRS Article, but you will both be taxed on your worldwide income. I believe there is an exemption for the first $80K in taxed income earned in Canada (I can't cite a source, but I have claimed this exemption for my spouse).
Once you are considered spouses under the US tax code then the gift isn't taxable at all according the current IRS literature. I am not sure of the tax implications on the Canadian side.
Of course, verify this information with an accountant or other tax professional before taking my advice.
If you are filing taxes as residents in the US, the citizenship will not come into account. You would be filing under the same rules as any other US resident, and limited to 26000. I'm no lawyer or accountant, don't take this advice to be professional advice from either of the two.
Keep in mind that that exceeding the $13,000 (or $26,000) limit doesn't, in itself, mean that you owe any taxes. It simply means that the gift amount counts against a lifetime exemption. I'm not sure what that is now (U.S. tax law keeps changing), but that amount used to be $1 million. That meant that the first $1 million of gifts to a person was tax-free.
In short, the $13,000/$26,000 dollar amount has to do with what you must report to the IRS, and what you must count as part of the $1 million exemption. It's only when you get past $1 million that you pay taxes. And if you're anywhere near that amount, you should be talking to a tax lawyer, not asking here.
Also: the official IRS page concerning gift taxes.