Hello Ajeh, please find my settings as below.
free shipping for international orders more than $100 works fine. but my problem is that, I want the user choose how to deliver the order.


Modules->Shipping->UPS
United Parcel Service

Enable UPS Shipping
True

UPS Pickup Method
CC

UPS Packaging?
CP

Residential Delivery?
RES

Handling Fee
0

Handling Per Order or Per Box
Box

Tax Class
--none--

Tax Basis
Shipping

Shipping Zone
--none--

Sort order of display.
10

Shipping Methods:
Nxt AM, Nxt AM Ltr, Nxt, Nxt Ltr, Nxt PR, Nxt Save, Nxt Save Ltr, 2nd AM, 2nd AM Ltr, 2nd, 2nd Ltr, 3 Day Select, Ground, Canada,World Xp, World Xp Ltr, World Xp Plus, World Xp Plus Ltr, World Expedite
1DM, 1DML, 1DA, 1DAL, 1DAPI, 1DP, 1DPL, 2DM, 2DML, 2DA, 2DAL, 3DS, GND, STD, XPR, XPRL, XDM, XDML, XPD

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Modules->Shipping->USPS
United States Postal Service

You will need to have registered a Web Tools account with USPS at their website to use this module.

USPS expects you to use pounds as weight measure for your products.

Enable USPS Shipping
True

Enter the USPS Web Tools User ID
710FLEAM6509

Which server to use
production

Handling Fee
0

Handling Per Order or Per Box
Box

Tax Class
--none--

Tax Basis
Shipping

Shipping Zone
United States

Sort Order
1

All Packages are Machinable
False

USPS Options
Display weight, Display transit time

Domestic Shipping Methods
EXPRESS, PRIORITY, PARCEL

International Shipping Methods
Express Mail Int, Express Mail Int Flat Rate Env, Priority Mail International, First Class Mail Int Lrg Env, First Class Mail Int Package, First Class Mail Int Letter

Debug Mode
Off
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Modules->Order Total->ot_shipping
Order Shipping Cost

This module is installed
true

Sort Order
200

Allow Free Shipping
true

Free Shipping For Orders Over
$100.00

Provide Free Shipping For Orders Made
international