Well..If it were me.I would make alliances with those who dislike Russia most.Hatred can often be a great morale boost.The more rage the better frankly.Unfortunatley,it can also cloud minds..Hmm..Gather those who hate russia,and then have some who are more non-involved spear head the operation.Seat the U.S. and U.N. at the head of the serpent,and use other countries as actual forces.Now,I won't lie,it will take many countries combined to beat Russia,they have a knack for not giving up.
I think that if they were surrounded (The Russians) on all possible fronts,then a combined army could slowly take over pockets of land.Target large infrastructure and slide your way in.For instance,have china and other Asian forces attack a stretch of land close to Asia,and then take western europe and invade the stalingrad area and creep inward,Japan being anisland can just fly some planes around,do recon.If Russia goes to rally in the east,rather than following them all the way through,move slowly,take the time to control civilian populated areas.If needed,conscript civilians to the armys of allies.I do not know how one would go about conquering Russia.They are formidable opponents,and I would much rather not test their battlefield strengths.
Do not worry Russia.Atleast one Canadian will have your back,haha.
Brothers in frost bitten freedom eh? hahaha