While most people will really appreciate you trying to speak their tongue, expect to be answered in English. At least in the Netherlands, this is not because people are so keen to practice their English (we get plenty opportunity for that), but because they don't want you to make an effort (and also because they feel uncomfortable having their own language mangled by your feeble attempts ).
This goes to the point where foreigners complain that it is impossible to learn Dutch, because the Dutch refuse to speak it with them...
I have the good fortune speaking German, as well as having a good working knowledge of French (I grew up in Canada, it was mandatory at my school), and have travelled in both countries (and in the rest of Europe as well). From my experience, many Europeans speak two languages (often more) and most (under 50's) will be able to communicate with you in English, especially in Germany (remember that the US military was stationed all over the country for almost 25 years after the war). People in France are a little more resistant to speaking English. But even there, people love to see foreigners making an effort to embrace local customs and that includes speaking the language. When all else fails, an open attitude and friendly, courteous approach will get you farther than any language course. Traveling from North America to Europe is not so crazy that you will feel like you're on a different planet. The best thing to do is to remain flexible and adjust your behavior towards others if they seem unreceptive towards you. Relax and enjoy yourself. Most importantly, don't take it personally if someone gives you the brush-off. Not everyone has had a positive (or any, if you're traveling to small villages) experience with foreigners.
As just about everyone has said here, learn a few words in both languages. After all, you wouldn't like it if a foreigner walked up to you in the USA and spoke to you entirely in their language, would you?? Of course not. Just the basics such as please, thank you, I can't speak French/German - sorry, little things like that are so much appreciated. I pride myself that I can say please, thank you, excuse me and I don't understand - in about 40 languages. Well worth learning and the locals will be so impressed that you're giving it a go.
As for pretending to be Canadian?? Whatever for?? Just be you.
Definitely learn some French. Some areas of France pride themselves on not speaking a word of English. Some people in some areas of France don't even speak French (Bretagne for example)! You will definitely get far more respect if you at least try to speak the language.
you try speaking English to Parisians, and see what happens! Parisians really don't appreciate people swanning into their city and speaking English all the time. Just a few words of French it'll go along way.
French people consider as incorrect people who speak to them directly in English. So try to learn some basic words like "Bonjour", "Excusez-moi" or "Merci" and believe me, french people will be charming and will try to help you, even if you don't speak french and they don't speak english.
[ Edit: Sorry, no promos please. ]