It seems to be legal to send medication to visitors in Canada, under the circumstances you specified, but I'm currently unsure which company will actually do so. If all else fails, I suggest contacting the US embassy in Canada for specific recommendations.
Visitors to Canada: Visitors to Canada may bring into Canada, on their
person a single course of treatment or a 90-day supply based on the
directions for use, whichever is less, of a prescription drug.
The drug must be for the individual's own personal use, for the use of
a person for whom they are responsible and with whom they are
The drug must be shipped/carried in one of the following: Hospital or
pharmacy dispensed packaging; Original retail packaging; or have the
original label affixed to it which clearly indicates what the health
product is and what it contains. A Visitor may import an additional
single unit, single course of treatment or a 90-day supply based on
the directions for use, whichever is less, of a prescription drug.
When a prescription drug is mailed to a Visitor, the drug should be
accompanied by some form of documentation indicating that the drug is
destined to a Visitor and/or the Visitor should be prepared to provide
documentation/written evidence (stamped passport, student/work visa,
letter from an employer/university etc) that they are a Visitor to
Canada when requested.
Tourist Importing Prescribed Medication to Canada
Visitors to Canada
may import into Canada, a single course of treatment or up to 90 days’
supply based on the directions for use. The doctor’s prescription must
be attached to the package. If you intend to import to Canada
prescribed medicine, please note:
Receiving prescribed medication in the mail When the medication has arrived and cleared by customs, you will receive a written
notification at the address indicated on the package. The carrier
notification will inform you where you should go to receive your mail.
To pick up your mail, present valid identification to prove that you
are a tourist, such as a passport stamp, Canadian tourist/student
visa, letter from Canadian school /or employer.
Health Canada prohibits the importation of prescription drugs by
courier when imported by Canadian residents for personal use.
The importation of prescription drugs for human use is strictly
regulated and is only permitted by certain entities. Under Section
C.01.045 of the Food and Drug Regulations, the importation of Schedule
F (prescription) drugs is restricted to a drug manufacturer, a
registered pharmacist, a wholesale druggist, a practitioner or a
resident of a foreign country while a visitor in Canada.
Please note that specific criteria must be met for visitors importing
prescription drugs. Also, at Health Canada's discretion, exceptions
may be made for Canadian residents returning from abroad who are on a
course of treatment and carry the prescription drugs with them upon
re-entry into Canada.