Fair comment about size of Germany - I'll rephrase - it's a dense place here. We're roughly 2.4 times your population but with only 3.5% of your land area; hence #7's comment; travel time's not a major issue with the incredibly efficient train system we have but it's all the stuff that gets missed out en route that can be problematic in planning an itinerary.
Seeing as you have Nuremberg xmas market on the list - which is E of Frankfurt, and assuming your flight home is ex Frankfurt, let's do a looped itinerary.
In 2 weeks, hit Nuremberg (2 days inc travel), down to Regensburg (2 days inc travel), down to Munich (4 days inc travel + a day trip to Dachau concentration camp and another day trip to Neuschwanstein castle), any of the villages outside Interlaken (Interlaken itself is rather dull, just a convenient transport hub) in central Switzerland for mountain scenery (3 days inc travel), Heidelberg (2 days inc travel), return on the last day to Frankfurt to fly home.
Of course, if you're from British Colombia the Swiss mountains may not appeal too much; in which case do (days in brackets include travel allowance) Nuremberg (2) Regensburg (2), Prague (3), Munich (4), Heidelberg (2), fly home.
Refer to http://www.bahn.co.uk to figure out how to get around. Tickets go on sale 3 months in advance on a first come cheapest served basis. You can compare the difference in price by picking a date 90 days from now vs the prices for travelling today to see what I mean.