Upvote:4
Will my previous technical difficulties cause me problems, either technical or with immigration, if I apply for an eTA now with a new passport (of a new nationality)?
Maybe.
When applying for an eTA now, should I include the number of the August 2015 eTA application, even though it is linked to a wrong passport number? Or just write N/A?
Yes, you should answer honestly and provide as much information as you can. You also have an oppoturnity to provide additional explanation (which you should do, as you have written here).
Should I take the issue proactively and apply even before I begin to think of a trip to Canada, so I can attempt to solve the issues well in advance?
There is a very significant likelihood that it will be simply approved. But yes, you should apply for an eTA as soon as possible. In case that the eTA is not instantly approved (within an hour), it will be reviewed by an agent and they may grant your authorization or request more information (e.g. copies of the emails you have sent them). It is not likely that you will be declined for the technical issues.
There is no way around an eTA application if you want to enter Canada unless you travel to the U.S. first and try to enter Canada by land travel or ferry.