cannibalization means having 2 or more pages optimized for the same keyword, or - in some cases - even for different keywords but which have the same meaning.
For example, let's say you have 2 keywords:
- self motivation tutorial
- learn how to motivate yourself
These 2 keywords - as you can see - are very different (different number of words and different words), but their intent is the same because they mean the same thing (how to motivate yourself).
If you were to create 2 different pages (1 page for each one of these 2 keywords) you will most likely run into cannibalization issues and google might not rank either page.
So, your best option is to group your keywords by intent and create 1 page for 1 intent, no matter how many words each one of your target keywords has, no matter what those keywords are.
In your case, it depends on which type of site you have: blog or ecom.
If it's blog, you can keep the pages already created, and make another page that talks specifically about Seiko (make it a 2-3000 words long page if you have enough content to talk about), and use the pages of those Seiko models as anchor texts to link to their individual pages. Also be sure to include a link to your main page (the one that targets the word Seiko) from each one of the individual pages (Seiko Alpinist, Seiko Prospex, etc)
If it's ecom.... well, I don't know in this case as I've never bothered with ecom sites, but probably that having a single page for all of your Seiko products would be the way to go. But I'm not sure, like I said. So, wait for someone else's reply...