Air Canada provides its own elites access to preferred seating but does not provide access to *Gold from other alliance member airlines. You can pay to access preferred seating either after booking or by calling AC reservations.

You can try your luck for a PE seat at the gate, but my experiences with AC would indicate that they don't tend to offer any extras to *G who are not AC elites outside of the standard *G benefits (eg, bags, boarding, lounges, etc.).