Data sims plus Canadian calling from UK?

[PhotoJim]

Hi,

Looks like our second UK visit will be in May 2015. Alas, my Camel SIM with Orange died after I forgot to top it up a couple of years ago. The trip will involve a week in London so coverage in the boonies is not really an issue.

Here's what we likely need:
- 2 iPad SIMs, 1-2 GB each - we use these in the field so we don't want to depend on WiFi
- data SIM (so I don't need to buy hotel WiFi), 2-5 GB should do; I'd consider tethering devices to one of the iPads but it's not my favourite solution. I have a lovely TP-Link mini-router so I can use unlocked data sticks I already have (3G) or buy a local LTE one (my LTE ones don't likely support EU bands).
- 2 voice SIMs, could just be voice/text but better if they come with 200 MB or more of data. If there were something like Orange's Camel that permitted cheap direct calling to Canada, that would rock; we found that so convenient last time we were there.

(I'll need the same for France [Paris only] so if there's some solution that will also work in France for some or all of these, that would be tempting, but I'm expecting to buy a similar set of solutions there.)

Suggestions?

Last time we used Orange for Canadian calling and O2 for UK calling and inbound calls (I didn't know about Orange until I got there, otherwise I might have used it exclusively), and I picked up T-Mobile for tethering. We didn't have tablets and my Treo smartphone didn't need a lot of data. Things have changed, though.

Thanks in advance!

Jim