Yes, you can double major in economics and political science. According undergraduate calendar, to double major you'll need:
1) Completion of any Level I program with a Cumulative Average of at least 6.0 including an average of at least 7.0 in
ECON 1B03 and
1BB3.
2) Completion of any Level I program with a Cumulative Average of at least 6.0 including a grade of at least B- in
POL SCI 1G06.
So basically, you need an average of 7.0 in Econ 1B03, and Econ 1BB3, and a 7.0 in Poli Sci 1G06. In addition, you'll need an overall average of 6.0.
Here are some useful links:
http://registrar.mcmaster.ca /CALEN...nt/pg1679.html
http://registrar.mcmaster.ca /calen...nt/pg1715.html
Good luck!