some CAN stocks IB doesn't offer

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from IB's faq

What Canadian securities are NOT available for trading?
IB does not offer Canadian Bonds and Mutual Funds. Due to technical or regulatory issues, IB also does not currently offer trading on Canadian warrants, stocks with symbols ending in .H and .U, and Limited Partnership (LPs).

I've searched around and cannot find what the .h, .u suffixes are for. Can anyone provide any info on that?
Any idea why IB doesn't allow it and when they will?
For say LPs & warrants, what do people use to buy those?
While I'm asking, how about any of the other exhchanges? What other offerings are missing at IB?

Thanks.