This paper assesses the precarious balance between the absence of political and legal oneness in federations and the respect of the rule of law. More precisely, it analyses how this balance is stricken by the Canadian Supreme Court. When it delivered the Reference Re Secession of Quebec in 1998, this Court explained how to make two constitutional principles complementary rather than antagonistic. This Reference has since guided the judicial comprehension of the rule of law in the Canadian federation. This paper first assesses the fundaments and the relevance of these judicial teachings. It then asserts that a differentiated and pragmatic appreciation of the rule of law, if some intrinsic components are found and guaranteed, is necessary in federations to avoid its plain and simple contestation. However, this paper warns the Supreme Court against what may be seen as a subtle unitisation of the rule of law as it would hamper its legitimacy in a heterogeneous federation such as Canada.