If you can obtain a dataset that has that grid, preferably at the smallest component level, then all you have to do is reference the attributes of the grid to locate the subsection your client provided, select it, and copy to your own dataset or map it. There are also options to export things to KML, JSON and other formats. QGIS is a free GIS software you could use to open base data in shapefile format and then get coordinate information from there. Working directly in a web mapping environment like Google Maps is beyond me.

I approach this from a GIS software perspective and looking at the underlying data needed. You can then get bounding coordinates or shapes from that (official?) source. Assuming the information you've been provided is whole quarters rather than individual lots with metes and bounds, the best thing would be to locate a base data layer that has the DLS grid for your area. In the PLSS your client would be right, the grid isn't regular. I'm not as familiar with the DLS and there are some differences to the PLSS. You say Canada, so I assume you're dealing with the Dominion Land Survey as opposed to the US Public Land Survey System - both use township/range/section references.

Township and range google earth