Proof of funds for a UK citizen visiting Canada for 5 months

I tried to find the information on Canada Border Services Agency' website but it was not very clear. Hence I'm answering this with my experience: CBSA is very strict but reasonable on these matters, in the end it'll be up to you convincing the agent you talk to that you are no longer intending to work in Canada, even if the opportunity arises, and that you can support yourselves or that you'll have means (like a flexible plane ticket) and intent (like a profound respect for Canadian immigration law and hopes to come back again in the future) to leave Canada if you run out of money.

They're very likely to inquire further when they see the combination of application but no IEC issued, long stay, and frankly very extremely low funds. The case is different from the IEC, as tourists you're expected to support yourselves without entering the Canadian labour market whereas IEC visitors can work to build up funds with which to travel. If you can only prove $4000 for two people, that's only $13 a day per person over five months. It's hard to do much and get by on that even eating peanut butter and crackers from Dollarama. If you can prove $8000 that's still only $27 per person per day, which is barely around the price of the cheapest hotels in all of Canada.

Primarily they'll be interested in you not working. Since you're staying for that long, having very good proof that you'll have a very low costs while visiting Canada (exact plans for accommodation with friends, camping, etc.) is key. It's possible they'll want to contact anyone who you say is providing you with free accommodation. They'll be extremely interested in the fact that you don't work, including working around the house in exchange for accommodation.