Hey there, for people who are applying for visas and such we must all meet a certain and exact requirements. Despite of you returning from the US doesn't mean they will look at that and go,"Oh wow, well she left the US, didn't overstay and such, we should allow her this visa."
You are to prove things like:
Quote from CIC (link: Cic.gc.ca)
To visit Canada, you must: have a valid travel document, such as a passport; be in good health; satisfy an immigration officer that you have ties, such as a job, home
and family, that will take you back to your country of origin; satisfy an immigration officer that you will leave Canada at the end of
your visit; and have enough money for your stay. The amount of money you will need
can vary with the circumstances of the visit, how long you will stay and
whether you will stay in a hotel or with friends or relatives. For more
information, ask the Canadian visa office in your country or region.
The most important thing is showing strong ties back home! However Ive read in some cases people had ties back at home, but are still rejected for the proofs of funds. I would recommend showing strong ties back at home like: Job(Get a letter from your employer of your return back) and also for the proof of funds you could have your sister write you an invitation "letter" statin that she would provide for your needs while you were in Canada.
What were your reasons that they rejected you by the way?