Okay.
I'll just use the example, say, of what I set up in my will. If I'm on my second marriage but I have children from my first, I want to make sure my wife is taken care of as long as she lives, as an income beneficiary, but I want the assets to go to my children from the first marriage.
The way things would work in my will right now is that I'd say she can participate in any income but she wouldn't have capital, and then the children get the assets when I pass on. My assets go to this trust on a tax-free rollover when I die, and then when she dies there is a deemed realization of gain, and that gain will actually go to her final return, and the assets go to my children. If my second spouse had family of her own, they'd end up having to potentially pay tax on assets that are going to someone else.
Now, the trust is jointly liable, but we're worried that the estate of my second spouse in my example is the one whom CRA is going to recognize as owing the tax.