Eligibility to work using my PR

It appears that you are still a Permanent Resident. As such, yes, you can enter Canada and work in Canada. There is, however, a serious problem. More on that below.

And, yes, your valid PR card will enable you to board a commercial flight destined for Canada. It is not, however, so much that your PR card entitles you to enter Canada, but your status as a Permanent Resident, that entitles you to enter Canada. And similarly, it is your status as a PR that entitles you to work in Canada.

In fact, whether the PR card was valid or not, as a PR you are entitled to enter Canada, and to work in Canada. If, however, your PR card was expired, or if you did not otherwise have a valid PR card in possession, while you would be entitled to enter Canada, the difficulty would be in getting to Canada . . . since you need a valid Travel Document authorizing entry into Canada in order to board a commercial flight destined for Canada.

All the PR card does is evidence your status.

The problem is inadmissibility due to a breach of the PR Residency Obligation.

You are obviously in breach of the PR Residency Obligation since you have been outside Canada for more than 1095 days since you landed (and that being within the previous five years).

This makes you "inadmissible."

Because you are inadmissible, when you approach the POE upon arriving at Canada, the most likely thing to happen is a referral to secondary, some questions in secondary relative to your absence from Canada, and upon confirming that you have been absent for more than 1095 days a 44(1) Report will be made followed, almost immediately (while you are still at the POE) the issuance of a Removal Order. Since you are still a PR, you are still entitled to enter Canada, and you have thirty days in which to appeal the Removal Order. During that 30 days, or during the processing of the appeal, you remain a PR and as such will still be entitled to work in Canada. If (well, actually "when" is more likely) you lose the appeal, upon losing the appeal the Removal Order becomes effective, that is "enforceable" and you will no longer be a PR at that point.

You can, however, argue H&C grounds at the time you arrive in Canada and attempt to convince them that you should be allowed to enter Canada without being issued a Removal Order. That gets more technical. If you can afford a Canadian immigration lawyer (not a consultant), that would be the thing to do: to contact an immigration lawyer for a consultation regarding your options.

You may want to review what it says in the applicable Operation Manual ENF 23 "Loss of Permanent Resident Status" (this is a link) and in particular see section 7.7 titled "Humanitarian and compassionate determinations" beginning on page 19, including especially the list of "factors for consideration" (on page 20).

In previous years, there have been a fair number of reports suggesting that PRs still within their first five years are treated fairly leniently by POE officials. This may no longer be true, however, plus even if you were to make this trip by the end of this month, you have gone past the threshold by a lot, making it more difficult. The Residency Obligation, after all, is quite lenient itself, allowing a PR to be absent for up to three out of five years.

But, your particular chances depend on your particular circumstances. To finish your education may be a good argument. Good enough? I don't know. If there are other factors (again, see the operational manual I link) in your favour, your chances are better: for example, if other members of your immediate family are living and settled in Canada, that too could help. But, again, obtaining the help of a lawyer in this regard is a good idea.