Howto generate the GeoJSON (or other format):
http://stackoverflow.com/questions/18523950/country-border-coordinate-data

Download the generalized Country borders from here: http://www.baruch.cuny.edu/geoportal/data/esri/esri_intl.htm. These are probably more detailed than you want (Canada has the most vertices at 3316), but is the only free rough border data set I could find online.

To get the coordinates from a shapefile as text, go to MyGeodata Converter

Run Vector Converter
Upload the zip file you just downloaded.
Check available operations
Export to GeoJSON
Download Zip file form MyGeodata Converter
Unzip the file.
Now you have the boundaries in GeoJSON format and can use a GeoJSON parser or a more simple text parser to get the coordinate data.



Get Shapefiles:
http://www.baruch.cuny.edu/geoportal/data/esri/esri_intl.htm#world

Utility:
http://converter.mygeodata.eu/