They could probably start with 2 routes and 4 planes, similar to OA that had leased 4 widebodies. They can even start by leasing. ATH-NYC and ATH-YYZ. They could even do hops in North America to scoop up pax from other Greek diaspora hubs. ATH-NYC-ORD, or ATH-NYC-YYZ, or ATH--YUL-YYZ. I know RJ and some other airlines do similar hops in North America.

In the winter when they may have reduced frequencies they can use the extra widebodies to LHR and other busy routes. Or more likely CPT/JNB would be a good choice in the winter, when it is summer there and there is also Greek diaspora.