+1(514) 937-9445 or Toll-free (Canada & US) +1 (888) 947-9445
Generally passport office is totally fine with dropping middle neames, esp if you have other docs without them. Just ask.

YMMV of course but I had no trouble with this ages ago and renewing etc.
In my case I was thinking of keeping my middle name, just that none of my other IDs (DL, Health Card) have it.
 
In my case I was thinking of keeping my middle name, just that none of my other IDs (DL, Health Card) have it.
I doubt it will be a problem if your citizenship certificate has it. Again, YMMV.

BUT: it's your responsibility to insist on the name you consider you own. If you use some other name, consistently, common law basically will take over under simple principal 'the name you use is your name.'*

*This simplifies excessively but still keep in mind. You should not be applying for documents under a name you don't want to be your name.