A quick and dirty way is to look at the implied volatility the underlying's front month options are trading at today.
Expect some cointegration risk, and expect your clearing firm to margin both sides of that trade as outright flat price risk. Just sayin'.
CAD is about 10 percentage points higher correlation to CL than PL. Actually, Zinc and Lead have significantly higher correlations to CL than PL at present on-the-run.