Creating EPub for iBooks with PDF FIles

I have a pdf file of a magazine that I print every month and am looking at the best way of getting it into iBooks and ultimately the iTunes store for others to download and view on iPads. I've tried a few things, but seem to be hitting a brick wall every time...

The pdf files are around 50 pages each, in A4 format. I have tried using iBooks author but their format is different to this and I can't seem to get my A4 page size in there. I realise now that IBA is more for digital publication and their layout differs from that of print. But is there any way I can do this?

I have also been trying to use Pages to output my ePub file, which works to an extent. I drag and drop my individual pdf pages into a new Pages word processing document, make sure thay are in-line and resize them to fit the page, which is A4.

I tried this with the first few pages, exported as ePub and imported via dropbox to my iPad 3. It shows up in my iBooks library, opens up and I can see my pdf pages, but they are a lot smaller than the ipad screen, and I cannot navigate around the page by pinching and zooming. When I try this, it selects the page "image" and highlights it in blue with the "copy, select, highlight" dialogue.

I have tried making the Pages document A3 size, resizing the pdfs in it to those dimensions and exporting the same, but in iBooks they are always a good third smaller than the size of the screen.

So is there any way I can get my A4 pdf files together as an iBook/ePub file that I can read in iBooks full screen?

Thanks!