Not specifically Sequel-related, but you can paginate any collection (even those will_paginate doesn't integrate with by default) using this:
require 'will_paginate/collection'
paged_collection =
WillPaginate::Collection.create(page, per_page, total_count) do |pager|
pager.replace(collection)
end
EDIT:
Try this:
require 'will_paginate'
require 'will_paginate/sequel'
require 'sequel/extensions/pagination'
page = params.fetch "page", 1
per_page = params.fetch "per_page", 3
@posts = Post.order(:id).extension(:pagination).paginate(page.to_i,per_page.to_i)