For in-depth information on Advance Rulings, please see Advance Income Tax Rulings and Technical Interpretations (IC70-6R9, 2019-04-23).
Advance Rulings are written statements "confirming how the CRA's interpretation of specific provisions of Canadian income tax law applies to a definite transaction or transactions that a taxpayer is contemplating. Rulings are generally requested by tax professionals on behalf of their clients. A fee is charged for a Ruling" (s.4 of the Advance Income Tax Rulings and Technical Interpretations)
The CRA does not publish their Advance Rulings, but they distribute them, in severed form to preserve taxpayer anonymity, to some tax publishers (see ss.51-52). The CRA cautions that Advance Rulings should be used with caution, as they "are not updated to reflect changes in the law..." and that "seemingly minor differences in facts and circumstances might result in a materially different conclusion..." (s.52).
Locating Advance Rulings
Because CRA doesn't publish these rulings, they can be difficult to locate. One source for rulings from 1974 to 1996 is Canada Income Tax Law and Policy, a looseleaf. Another source for historical Advance Rulings is the Canada Income Tax Guide.