So this is easy now. However, following is the guideline for your information.
Quoted from FE Circular No 09, dated Aug27/2012
"04. In terms of paragraph 1(ii), chapter 12 of Guidelines for Foreign Exchange Transactions‐
2009, Vol‐1, ADs are allowed to release foreign exchange in the form of cash up to US$ 2000 at any one
instance out of travel entitlement to Bangladeshi national proceeding abroad. However, confusion
arises as to whether ADs can release balance of the entitlement in the form of cash in other currencies.
This is to clarify that ADs may release USD 2,000 in cash and the remainder in other freely convertible
currencies out of the prescribed entitlement i.e., US$ 5,000 for travel to countries other than SAARC
member countries and Myanmar."
I talked to HSBC bank few days back. The guy who does this, told me that we can purchase USD2000 + equivalent 3000 usd in other currencies, i.e., GBP or EUR (canadian Dollar not available to anyone)= Total Equivalent USD5000 per passport (adult) and all in cash we can purchase from bank now. So legally you can buy 5000 equivalent USD per passport thru endorsement to your passport. For Child - the limit will just be half. For dollar purchase, City bank rate is better - suggested by sohel4math bhai (also shumon bhai). Canadian Dollar purchase korte gele Money exchange chara kono upai nai. Dibakar bhai er moto onekei tai koresen, i.e., USD 2000 from bank via endorsement + rest in Canadian Dollar (as much as possible - no limit). Now decision is yours.