The US sets the price it pays for Canadian oil, a discount from the market price.
I don't know about timber, but the US maple syrup industry is healthy, just unable to keep up with demand. I think that's a consequence of geography and the time investment required to get mature trees, not Canada undercutting.
I don't really know how the discount is built into the price, but it's a result of the fact that only about 10% of the oil Canada produces can make it to a port to be sold to non-US buyers.
The price is “discounted” as in “it's cheaper than the global market price”, because of the shipping difficulties, but it's not a “discount” in the sense of “americans get a discount because we're nice neighbours and they have a coupon”.
A common point of political contention up here are various pipeline issues, precisely because it potentially permit access to more markets, improving the sale price. (However it would also raise the price of gas in Canada for the same reason, with all the implications that comes with that).
I don't know about timber, but the US maple syrup industry is healthy, just unable to keep up with demand. I think that's a consequence of geography and the time investment required to get mature trees, not Canada undercutting.