Canadian work permits generally fall into two categories, and the distinction shapes almost everything about how you can work once you have one.
Employer-specific work permits
An employer-specific work permit authorizes you to work only for the employer named on the permit, in the position and location specified, and typically for a defined duration. Most employer-specific permits are supported by either a positive LMIA or an LMIA-exempt offer of employment. If you want to change employers while on this type of permit, you generally need to apply for a new work permit before starting the new job — you cannot simply switch employers on the existing permit.
Open work permits
An open work permit allows you to work for almost any employer in Canada, in almost any occupation, without needing a specific job offer or LMIA to support it. Open work permits aren't available to everyone; they're issued in specific circumstances, such as to spouses of certain work or study permit holders, to some Post-Graduation Work Permit holders, to inland spousal sponsorship applicants, or under specific international programs like International Experience Canada. A small number of employers are restricted from hiring open work permit holders due to past labour standards violations, so even “open” permits carry limited restrictions in practice.
Which one applies to you
You don't generally choose between the two as a matter of preference — your circumstances determine which category you're eligible for. Someone with a specific job offer from a Canadian employer will typically be looking at an employer-specific permit (via LMIA or an exemption), while someone eligible through a spousal, post-graduation, or reciprocal program route may be eligible for an open permit instead.
Why the distinction matters practically
Job security and flexibility differ significantly between the two. An open permit holder can change jobs freely without new paperwork; an employer-specific permit holder generally cannot, and losing that job can mean losing authorization to work until a new permit is secured. Anyone weighing a job offer against their permit options should understand which category they'd be entering before accepting.