interesting - I wonder, I suppose, maybe and perhaps are almost interchangeable in a lot of circumstances in English, but create very subtle differences in meaning although the listener won’t really notice much difference.
I wonder if the road will be busy
I suppose the road will be busy
Maybe the road will be busy
Perhaps the road will be busy
I imagine the road will be busy
Ah yes, that rings a bell. Thanks!
And with that spelling I think I found the place I had looked it up before again 
Gweiadur.com gives it as “ys gwn i” with “tybed” as an alternative.
(However, I think I first saw it (as “sgwn i” ) in Gareth Kings bumper book of Welsh grammar 
)
There’s an article about the advert, some of which I understand (it’s written for native speakers, and a wee bit challenging for me at the moment!), on Golwg360, if anyone’s interested.
You can use the VOCAB button at the top to help with the words. Having said that why is it on the BBC or on Golwg, that the Vocab button never seems to have a translation for the words that you really want to know.
I read it through and then went back to the VOCAB button to find out what the following meant:
“mae’n nodi bod angen herio ystrydebau’r maes” The one word that really stands out as tricky and obviously doesn’t get a translation is “ystrydebau” - Fortunately google is on hand and says: “stereotypes”
“Cliché” and “Truism” are alternatives offered by Gweiadur. (But “stereotypes” seems to fit here).