Return of Capital for US MLP or ETF - Tax in Canada

[Sparkling451]

I'm a Canadian citizen living in Canada. I have no residency in the US.
As I understand it, any distributions from a US MLP or a US ETF that includes Return of Capital is taxed in Canada as normal dividend income, regardless of the tax withholding and implications in the US.
My question is does the Return of Capital also have to be used to calculate the Adjusted Cost Base of the MLP or ETF when it is sold and reported for taxation in Canada? That would tax the income once as a dividend and once as Capital Gain.
I've searched a lot for an answer. Any help will be greatly appreciated.