- Q1 Do I need a specific visa to enter Ireland?
The Common Travel Area (CTA) consists of the UK, Guernsey, Jersey, the Isle of Man and Ireland. Non-EU/Schengen citizens receive an Irish entry stamp, even if arriving from the UK. For visa-free nationals, this lets them stay in Ireland for max 3 months. The time those without a UK visa are allowed in Ireland also includes the rest of the CTA. For travellers visa-exempt for both the UK and Ireland, the visa exemption is 6 months in the UK but only 3 months in Ireland, meaning if a Canadian citizen visitor enters the CTA through Ireland, they'll only be allowed 3 months in the whole CTA. https://travel.stackexchange.com/questions/138745/what-do-non-eu-schengen-citizens-need-to-do-when-travelling-within-the-common-tr
- Q2 Is there a way to extend my working holiday?
There is no 14 day grace period because grace periods only apply to categories of visa eligible for extension. A Tier 5 Youth Mobility Visa is valid for two years, no extensions are allowed and you must leave the UK before your visa expires. https://www.gov.uk/tier-5-youth-mobility If you don’t leave by the expiry date, you will be out of status and considered to be overstaying https://www.davidsonmorris.com/overstay-in-uk/
Prior to the COVID-19 crisis, you could have exited the UK to a nearby Schengen country and re-entered as a visa-free national for up to 6 months, provided you could satisfy UK Immigration, if asked, about your purpose in returning and your intention to leave (see V4.2 https://www.gov.uk/guidance/immigration-rules/immigration-rules-appendix-v-visitor-rules). Given the impending EU travel ban https://www.businessinsider.com/coronavirus-eu-to-ban-non-essential-travel-for-thirty-days-2020-3 since you are not an EU citizen, and will not be a long-term resident after your visa expires, a visa run to Schengen is no longer possible.
Your best option is to return to Canada.