I thought it would interesting to post a link to DFAIT (Canada’s ministry of Foreign Affairs) info section on dual nationality.
Some interesting points they make:
You are a dual citizen if you are recognized by more than one country as a citizen. In some cases, you may not be aware that you are a citizen of another country. Dual, or multiple, citizenship may occur by choice or default and result from:
an application for foreign citizenship
your place of birth
family connections, including place of birth of one of your parents or even grandparents
marriage to a foreign national
extended residency in a foreign country
You may be legally required to register for military service and to respond to call-up orders in the country of your other nationality. This obligation may be enforced even if you are just visiting that country and permanently reside in Canada. Some countries do not accept ignorance as an excuse for failure to comply. The consequences could be imprisonment or immediate induction into military service the next time you arrive in the country or attempt to leave. Even dual citizens who have passed the age for military service may be considered defaulters for failing to report at the required time. (My Note: Roger is probably more of expert on this than me but US Citizen males of certain ages are still required to “register” with the Selective Service Administration)
You could have tax obligations not only in Canada but also in the country of your second citizenship. Taxation arrangements between countries are complex, and you should discuss these obligations with your financial and/or legal advisers.
But they give an interesting piece of advice:
Always use your Canadian passport if possible, especially when entering the country of your second citizenship. Note that you cannot use a Certificate of Canadian Citizenship instead of a Canadian passport to travel abroad. A Certificate of Canadian Citizenship is not a travel document. A Canadian passport is the only reliable and universally accepted travel and identification document available to Canadians for the purpose of international travel. Canadian citizens returning to Canada who present other documents, such as a Certificate of Canadian Citizenship, birth certificate, provincial driver’s licence or foreign passport, instead of a Canadian passport, may face delays or be denied boarding by transport companies.
Using your Canadian passport may provide the basis under which Canada can provide you with consular assistance if you run into problems. You should also obtain a visa, if that is required for entry by Canadian citizens, and always present yourself as a Canadian when dealing with local authorities.
Now of course from what we have discussed the US is not very fond of people in these circumstances entering on Canadian passports(and I believe if you go to DFAIT’s travel information sheet on the US this is mentioned). However, I think this is a very good advice especially as to third countries.