Lucky you, fortunately it's easy for you to accomplish:
§ 61.153 Eligibility requirements: General.
To be eligible for an airline transport pilot certificate, a person must:
(a) Be at least 23 years of age;
(b) Be able to read, speak, write, and understand the English language. If the applicant is unable to meet one of these requirements due to medical reasons, then the Administrator may place such operating limitations on that applicant's pilot certificate as are necessary for the safe operation of the aircraft;
(c) Be of good moral character;
(d) Meet at least one of the following requirements:
(1) Holds a commercial pilot certificate with an instrument rating issued under this part;
(2) Meet the military experience requirements under §61.73 of this part to qualify for a commercial pilot certificate, and an instrument rating if the person is a rated military pilot or former rated military pilot of an Armed Force of the United States; or
(3) Holds either a foreign airline transport pilot license with instrument privileges, or a foreign commercial pilot license with an instrument rating, that—
(i) Was issued by a contracting State to the Convention on International Civil Aviation; and
(ii) Contains no geographical limitations.
(e) Meet the aeronautical experience requirements of this subpart that apply to the aircraft category and class rating sought before applying for the practical test;
(f) Pass a knowledge test on the aeronautical knowledge areas of §61.155(c) of this part that apply to the aircraft category and class rating sought;
(g) Pass the practical test on the areas of operation listed in §61.157(e) of this part that apply to the aircraft category and class rating sought; and
(h) Comply with the sections of this subpart that apply to the aircraft category and class rating sought.
Written test and checkride, that's it.
There is an agreement between the US and Canada as far as transferring or converting each other's certificates, did you look into that?