As with any other application, but especially so for a government position, it's crucial to fully understand all the details of the job description and how your skills and experiences best align with the role. Having that understanding, it'll be useful when crafting a resume and cover letter and, hopefully, an interview. It's also crucial to research the department or organization you're applying for to understand its mandate, how it might operate, and where it fits in more broadly to government and Canadian society. I'd suggest noting all this research down as it helps when you get to important steps like your interview.