When submitting your manuscript to a publisher be sure to enclose a stamped, self-addressed envelope (SASE) large enough that your material can be returned to you. By tracking your package on the Canada Post website, you will be aware of when it was delivered.
But is it sitting, unopened, with the rest of the mail? To save having to wonder about that question, I also include a stamped, self-addressed postcard with my submission. It can be dropped in the mail when the package is first opened.
Always keep a record of your submissions. Note what you sent (3 sample chapters and synopsis, complete manuscript), to whom you sent it, the date it was mailed and the cost of the postage. I also make a note if I had to send out a further query and the date of that letter.
If the publisher's website indicates that they will get back to you in 4 to 6 months, it's perfectly ethical, after that period of time, to inquire about the status of your manuscript. Is it still being considered? Send this query by regular mail. Do not email or telephone, unless you have been instructed by the publisher to do so.
Your manuscript may be one of hundreds they receive each month. Be prepared to wait, and while you do, get on with your next writing project.
Congratulations! You've taken the first step towards publication. It will never happen while your manuscript sits in your desk drawer at home.