We have no particular opinion other than we generally prefer natural law entities over statutory ones. In addition, please be aware that good Natural Law Trusts can operate as foundations. The only possible disadvantage we can think of is that if you are accepting donations and you want the donors to be able to write off their donations on their tax returns as tax deductible, then your foundation may have to be a statutory entity. We are assuming that's what you are referring to in Canada, as a Private Interest Foundation. In the US, a 501(3)(c) can operate as a foundation and be tax exempt, but it is a statutory entity and thus is subject to a long list of regulations. It does, however, offer the benefit that donors to it can have their donations be tax deductible.
If your foundation is philanthropic and will be giving donations rather than receiving them, then a good Natural Law Trust could be set up that way and would be far superior, in our opinion, because it would have no tax agency or government filing requirements and would therefore be subject only to natural laws -- i.e. don't lie, don't steal, don't violate the basic rights of others, etc. It would be free of the millions of ever-changing statutes legislated by politicians and lawyers every year.
Or, if your foundation will be receiving donations, but you don't care whether the donations will be tax deductible for the donors, then too, the Natural Law Trust would be superior.