Once you understand how the Canadian stumpage system works, it's hard not to see it as a government subsidy to the industry and workers.  Rather than auction off timber rights, under stumpage the government collects fees based on the lumber companies' difference between production cost and selling price.
Under an auction-based system (used in the USA), the lumber companies bear the risk of price fluctuations.  If prices drop due to excess supply, they are incented to reduce production.  However under stumpage, the Canadian producers have no incentive to reduce production, and their profit levels are assured, because if the lumber prices drop, the stumpage cost drops so they remain whole.  It is an insurance scheme for industry profits - they have transferred the risk to tax payers.  The gov collects less revenue from selling its wood, but what do they care so long as lumber companies and unions are happy?  No wonder USA is upset, their government won't reduce fees when prices drop.