The OCA has a "late vocations program," generally for guys who are interested in the diaconate, but who already have careers and families, and for whom moving to a seminary is not always possible or practical. A deacon at my parish was ordained last Dec 03, and completed his preparation for the diaconate in this manner. I am looking into this program for my future as well. Of course, the "late vocations program" has to be under the direct supervision of one's priest, and before any studying and preparation can begin, it must be approved by the Bishop and/or by the OCA coucil of bishops altogether. I believe that if one completes the "late vocations program" and is ordained a deacon, and wants to then be a priest, it is almost always required to spend at least some time at a seminary.
I am not sure if other Orthodox churches in the USA/Canada have similar programs.
As far as I know, being tonsured a Reader or becoming a sub-deacon does not require as intensive a program. Best to inquire directly with one's priest about these matters.