If you've got a smart phone you can buy a UK SIM and install that. A good company is GiffGaff as they will send you the SIM in the mail so you have it as soon as you arrive in the UK. The difficulty with this is that
you don't have your usual mobile number which will be a pain for people trying to contact you and if you get 2 factor authentication via text. So take a look at your local phone/data provider and they will have an international plan. These are not cheap, but they are getting cheaper and they are convenient. FYI AT&T in the US has an international plan that lets you use your regular plan overseas for $10/day with a cap of $100/month. So for a 6 week trip something like that might be ok. A GiffGaff unlimited data plans cost about $50/month, but is not as convenient.
I do not know if you can get a Google Voice account in Canada or not, when I did over a decade ago it was only available in USA. You can get a local phone number when you do that. And that is a Voice Over Internet Protocol (VOIP) way to make phone calls using either wifi or a data plan. Over a decade ago I called one of my credit card companies in USA from Budapest when my card stopped working. And in Reykjavik I called one of my credit card companies in USA when that card stopped working. So, I know that Google Voice works in most foreign countries. And used it several other times, for example on my Pacific Coast tour the two of us with different cell companies both did not have cell service, but I could make a call using the wifi at a restaurant.
Your phone has to be turned on, with wifi or data active for someone to call you, I always travel with phone off or in airplane mode, so I do not get calls. But at least you can call out. Calls to you, you get an e-mail with the voicemail message.
I have two cell phones, one of which has a data-only sim card. I have gotten in the habit of only using that data phone, with VOIP to make calls when I travel. Sometimes, if I know that I might get a call from someone I know, I will leave the data plan on and active so it can ring and I can answer. My other cell with a regular cell number and tiny data plan often is turned off, only carried when I go for a bike ride in event of emergency. It is often stored in my handlebar bag. I can't remember the last time I actually used that as a cell phone to call someone or be called.
My home phone (land line) since this past Nov has also been VOIP, and I can even answer a call on that line on my cell with the data only sim card, thus that phone actually has two phone numbers, both are VOIP, neither of which is a "cell" number.
In other words, there are a lot of options these days for calling people. When I planned to do LEJOG, my intent was to buy a cheap Android phone with UK frequencies. I planned to buy the phone itself while in USA so that I could install the apps I wanted on it before I left home using wifi. And once in the UK, I planned to buy a data only sim card, if a data only one was available.
If you get a Google Voice account with a phone number, call someone every couple months, otherwise Google might retract that phone number from you if it is not used for a long time.