MdPkR,
i cannot fully answer your questions, but can make some comments based on my experience on applying for a work permit.
- my application was processed in 18 days + 3 days mailing time from Vienna to the Netherlands. The website says 20 days excluding mailing time, so was in fact ahead of time. You see from other comments in this forum that for some people it took longer than the initial estimate.
- note that if you submit in person, you'll be without your passport to return to Germany. In theory, you're not allowed to travel without it, even though both countries are within the Schengen space (only EU nationals can travel without a passport). In practice, if you travel by land (car or train), it is very unlikely that police will stop you to check for documents, unless you're doing something obviously wrong. If you fly, then the airline may refuse you boarding the flight. You can use DHL to send documents, it is a bit expensive but it gets there next day (saves a couple of days compared to normal mail), is very secure and you can track delivery online. They returned my passport by registered mail that could only be delivered to myself in person (nobody else, I had to show my ID).
-not sure if the american visa helps or not. in theory it should not make any difference, in practice maybe it does.
- don't see any problem regarding your wife visa (if they grant yours, they will most likely also grant her a visa). I'm not even officially married and my partner got an open work permit as well without submitting any additional document.
it would be better to apply after your German visa is extended, so it becomes clear that you have no intention of immigrating illegally. If you apply before your visa is extended, I would include a letter and any other documents explaining your situation, that you expect to continue in Germany (or whatever you plan to do after your trip), etc... to demonstrate you will not stay in Canada, basically you have to provide good reasons why you would not stay there. I know how this may sound, but the officer has to be convinced you will not stay there and he/she only has a limited amount of time to look at your file - I would definitively be on the safe side.
hope that is of some help to you.
Please post your timeline here for the benefit of future applicants. (when you applied, how long it took, when you receive it back).