The Canadian dollar was falling well before the current oil price drops. WTI peaked around $108 in June 2014, but the CAD has been falling fairly steadily since Sept 2012, when it was over $1 USD. Yes, the most recent fall has been happening at the same time as oil prices have been falling, but it's been falling at about a cent a month, compared to about half a cent a month it was falling for the two years before that(when oil prices were basically flat).

Russia is better known for gas, because gas is harder to ship, and more dependant on pipelines - oil can be shipped by tanker or rail more easily. As such, if Europe gets Russian oil cut off it can buy from the Saudis, but if Russian gas gets cut off, they have many fewer options, and a cold winter. That said, LNG tankers are getting more common(largely to take advantage of the cross-Atlantic arbitrage between the frack-happy Americans and the enviro Europeans), and will alleviate that problem somewhat.

Gas prizes are pegged to oil prices.