It does look like Niagara Falls sent you to MB SK because MB SK has an earlier availability. I haven't seen a lot of posts on that office, but the ones I've seen are from people with normal processing. Definitely let them know during registration that you have the upcoming travel. You should also mention it when you email them your signed oath form, and also attach the supporting letter.
See the Citizenship Certificate After Oath thread, especially the more recent posts, for a better idea of how long it's taking in the different offices these days. At least you're not with the Winnipeg office, which seems to be a separate one from MB SK and has been very slow even for people who requested expedited service - you can read the posts from @warrior30 who is still waiting since October 17 oath and had to miss his sister's wedding!
The whole Winnipeg office is not bad, it just has a few bad egg clerks who are on an absolute power trip and will decline any expedited request you make with proof. Family urgencies are not important for them. Not just that, they will not reply to your emails and will never answer what you ask.
Your expedited request will be denied even when you provided proof. Then your oath form email will be lost and you will be asked to resend your oath form after 4 weeks of oath ceremony. And then your certificate will be sent by ordinary mail even when you requested Express Post with tracking and willing to pay for shipping. And then it will be lost by Canada Post on the way.
This is my story so far. What a joke!!