Russia has allot of experience with wildfires it has the largest and densest northern forests in the world combined with a permafrost that holds insane amount of methane and other carbohydrates.
Climate change and forest fires are huge national security issue to Russia and if they go out of control it can cause horrible damage to Russia and even then entire planet as it can cause a Permian extinction style event which happened before when the Siberian carbon traps went up in flames. https://en.wikipedia.org/wiki/Permian%E2%80%93Triassic_extin...
Russia has been dealing with huge wild fires every several years https://en.wikipedia.org/wiki/2015_Russian_wildfires https://en.wikipedia.org/wiki/2010_Russian_wildfires
They are one of the few countries that designs and builds dedicated firefighting aircraft designed to combat large forest fires. https://en.wikipedia.org/wiki/Beriev_Be-200 And while they might be arseholes on the political scene otherwise every time there is a large scale fire they do extend their hand and come in with serious help.
Inviting a totally foreign country in which you're in a) fighting a proxy war with in yet another part of the world; and b) fighting a passive battle for northern sovereignty/control with seems like an incredibly stupid idea.
Canada has many forest fires on the go every year and are generally only worth fighting when they threaten communities. Forests are meant to burn. I have friends who work in emergency fire fighting in Saskatchewan and they have not been deployed to the Northern fires because it is not the problem the media is making it out to be!
Drought conditions and the heat traps that are cities prevent proper rainfall which stops them and changes we've made to the landscape can prevent burn outs which also make fires last longer.
And more importantly while forest fires are natural it doesn't mean it's good, we had at least one fire related extinction event, and even considerably smaller scale fires can be disastrous to humans so while it's true that to some extent the policy is let it burn in this case it's not longer really the case.
And while I would also agree that Canada is in a political muck with Russia it doesn't make sense to deny their help, Israel accepted Turkey's help to combat forest fire when their relationship was arguably at the lowest point shortly after the flotilla incident. Governments should know when it's a good time to put a halt to their differences and emergencies are as good as an excuse as any.
P.S. With forests being natural carbon traps climate change is now just as important factor as threat to communities and livelihood with the amount of CO2 were putting into the atmosphere we might not be able to longer afford for forest fires to take their natural course if we actually want to start reversing some of the changes we've made. This isn't some clear cut case, and in this case it seems that Canada does take help from certain countries but for some reason refrains taking it from others and in such cases politics should really be the last thing on your mind.
It's difficult to top the US in terms of foreign policy assholery though.
I never had this thought until now, but the things you eat are called carbohydrates whilst the things you burn are called hydrocarbons.
The fire presented a risk right at the beginning and seemed to spread into populated area's faster than could be responded to, once that risk was no longer present outside assistance was not required.