1ですが、ガバメントサイトの説明を見つけたので貼っておきます。
https://www.canada.ca/en/employment-social-development/programs/ei/ei-list/working-while-claim.html
How working affects your claim
If you earn money while receiving EI benefits, you can keep 50 cents of your benefits for every dollar you earn, up to 90 percent of your previous weekly earnings (roughly four and a half days of work). Above this cap, your EI benefits are deducted dollar-for-dollar.
You are not eligible to receive EI benefits if you work a full week, regardless of the amount you earn. However, this will not reduce the total number of weeks payable on your claim.
Example 1
John was laid off when the grocery store where he worked shut down. His weekly earnings at the grocery store were $500, so his weekly EI benefit rate is $275 (55 percent of $500). He has found a part-time job at a restaurant, where he works three days a week and earns $300 per week.
As a result, his $275 in EI benefits are reduced by $150 or 50 cents for every dollar he earns at the restaurant ($300 ÷ 2 = $150). This brings his total EI benefit to $125 ($275 – $150 = $125).
In the end, John takes home $125 per week in EI benefits plus his part-time wages of $300, for a total of $425.
Example 2
Melissa got sick, stopped working to recover from her illness and applied for EI sickness benefits. Her normal weekly earnings were $850, meaning her EI benefit rate would be $468 per week (55 percent of $850).
Melissa was off work for three weeks before her doctor wrote a note saying she could return to work part-time for two weeks, and work full-time after that. Melissa returned to work part-time, working a day and a half per week and earning $260 per week.
In her first week off work, Melissa served her one-week waiting period and was not paid any benefits. During the second and third weeks that she was off work, she received $468 in EI sickness benefits.
For the fourth and fifth weeks, Melissa worked part-time and her benefits were reduced by $130 or 50 cents for every dollar earned ($260 ÷ 2 = $130). This brings her total EI sickness benefits to $338 ($468 – $130 = $338). For the weeks she worked part-time, she took home $338 in EI sickness benefits plus her part-time earnings of $260 for a total of $598.
Melissa is not paid any sickness benefits in the sixth week because she returns to work full-time.
Exception for some employees on paid short-term disability leave from work
Is your employer registered in the Premium Reduction Program (PRP)? Employees who become ill or injured need to first make use of their employer's sick leave plan before receiving EI benefits. If you are receiving wage loss indemnity or paid sick leave from an employer registered in the PRP, your earnings will be deducted differently. Find out more about the Premium Reduction Program.