Same way the US squares away their federal system. Some areas of law are federal, some are provincial. Quebec’s use of Napoleonic Law only applies to those areas covered by the Quebec Courts. Federal matters are handled in Federal Courts, so they’re not subject to Quebecois legal principles.
Off topic but how does Canada square away their English system with the one province under the French system? They’re nearly opposite systems.
Criminal law in Quebec is still based on the federal common law, it’s just matters of provincial jurisdiction that are under civil law.
Louisiana runs off French civil law. They work around it.
Same way the US squares away their federal system. Some areas of law are federal, some are provincial. Quebec’s use of Napoleonic Law only applies to those areas covered by the Quebec Courts. Federal matters are handled in Federal Courts, so they’re not subject to Quebecois legal principles.