Unsure about difference Canadian English to American English for have showed/shown

I'm reading the sentence "I've showed strength. Haven't I showed them a clear path?
My personal feeling as a Canadian is that the word should be shown after have, is that correct? Is it any different in American english?
Thanks for any help.

• :-?

For the US, the dictionary lists both "shown" and "showed" as the third form, though "shown" sounds more natural to me.

I prefer "shown" and similar words in these situations. But not all do.

Showed, I think. But it's such a minor point.

There are many words like that: lighted or lit, dove or dived, spelled or spelt, gotten or got, whilst or while. It boils down to personal preference. There's no need to be consistent, either: I prefer lit, dove, gotten or got depending on context, and spelled. Why, I can't really say.

Except it's "while". Always "while", dammit! ;-)