I wouled like to ask for the flight ticket from lao to canada

Lao citizens need a temporary resident visa (this is the official name Canada gives to visitor visas) to visit Canada. You need to obtain the visa before you depart.

You do not need a visa to transit through Seoul and remain in the airport transit area. You are allowed to leave the airport on Korea's transit tourist program for a brief tour of the city, if you have sufficient time between your flights.

You will likely be denied boarding, or denied entry to Canada, if you have a one way ticket.

Timatic, the database which airlines use to verify passenger travel documents, states in part:

Korea (Rep.) (KR)

TWOV (Transit Without Visa):
Visa required, except for Passengers transiting through Seoul (ICN) with a confirmed onward ticket for a flight to a third country within 24 hours. They must stay in the international transit area of the airport and have documents required for the next destination.

Visa required, except for Passengers transiting through Seoul (ICN) with a confirmed onward ticket for a flight to a third country within 72 hours. They must:

• join a transit tour organized by Seoul (ICN), and
• have documents required for the next destination.

(For Canada, visa exemptions exist but none apply to you, so they are not shown here.)

Canada (CA)

Warning:

• Visitors not holding return/onward tickets could be refused entry.